JavaScript interop, but how ?

[Roger Gilliar]

I'm still having troubles to figure the right way to use JSON objects in Ceylon. For example how do I iterate over all properties ? How do I check if a property exists ? How to convert a JSON object to something more Ceylon like a stream of pairs ?

[Enrique Zamudio]

you can still call the methods in the JS Object class, like \iObject.keys(x) or x.hasOwnProperty("foo") for example.

Iterating over an object's properties is a little more cumbersome since there's no way to generate a for(p in o) loop, so in Ceylon you need to do something like this:

dynamic props = \iObject.keys(x);

for (String s : props) {

  print("``s`` -> ``x[s]``");

[Gavin King]

Here's an example in the Web IDE.

http://try.ceylon-lang.org/?gist=eb467e4cf7f812861d81a080d7fbb249

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[Roger Gilliar]

Thanks, I'm using underscore now and that works quite good. One thing I do not understand is the meaning of Anything in a dynamic block. Assigning v1 and v2 works but v3 gives TypeError: Expected ceylon.language::Anything (Record.ceylon 20:26-20:31)

 

value fields = HashMap<String, String>();

dynamic {
     obj = data
     for (k in _keys(obj)) {
         String v1 = k;
         v2 = obj[k]
         Anything v3 = obj[k];
         fields.put(k.lowercased, k)
     }
 }

[Gavin King]

Right, a plain JavaScript object isn't an instance of any Ceylon
class, nor even of the class Object, until you assign it to a dynamic
interface type. This is discussed in the tour here:

https://ceylon-lang.org/documentation/1.3/tour/dynamic/#dynamic_instantiation_expressions

So this code results in an error, since point doesn't even have the
operations of Ceylon's Object type:

dynamic {
dynamic point = dynamic [ x=1.0; y=2.0; ];
Anything any = point;
}

However, the following code is OK:

dynamic Point {
shared formal Float x;
shared formal Float y;
}

dynamic {
dynamic point = dynamic [ x=1.0; y=2.0; ];
Point typedPoint = point;
Anything any = typedPoint;
}

It's acceptable because the assignment of point to Point "dresses" the
JavaScript object as a Ceylon object of type Point.

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[Stephane Epardaud]

You're missing a few semicolons at the end of your lines that's why, I think.

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[Roger Gilliar]

I changed the code a bit. The real problem seems to be, that a Date value can' be assigned to Anything. Is therefore a Date object considered a plain JS object ?

value fields = HashMap<String,Anything>();
value ignore = ["$$", "getT$name", "getT$all", "string", "$prop$getString", "hash", "$prop$getHash"];

    dynamic {
        obj = data;
        for (k in _keys(obj)) {

            if (!ignore.contains(k)) {
                dynamic v = obj[k];
                try {
                    fields.put(k.lowercased, v);
                } catch (Throwable t) {
                    print("-----");
                    print(k); // gives timestamp1
                    print(v); // gives Tue Oct 04 2016 16:16:55 GMT+0200 (CEST)
                    print(_isDate(v)); // gives true
                }
            }
        }
    }

[Gavin King]

Right, yes, a JavaScript Date isn't an instance of any Ceylon class.

Here's how to convert a JavaScript Data to a ceylon.time DateTime object:

http://try.ceylon-lang.org/?gist=6a00f7c56bcd2db586ba543a18ff9ebd

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[Roger Gilliar]

Just out of curiosity: Why is a Date not an instance of a Ceylon class, but a JS string is an instance of some Ceylon class ?

[Gavin King]

Well, String is defined in the Ceylon language module and the compiler
and runtime do a bunch of special magic to make JavaScript strings
appear to be instances of String. But there's no Date type in the
Ceylon language module to do any sort of equivalent mapping.

On Sat, Dec 3, 2016 at 7:35 PM, 'Roger Gilliar' via ceylon-users

> https://groups.google.com/d/msgid/ceylon-users/8c8faea3-89f5-4857-a203-ec4be12d5397%40googlegroups.com.